This invention relates generally to hypodermic needles and syringes, and more particularly the invention relates to a spring clip lock which can be used to convert a plastic hypodermic syringe into a single-use, difficult to reuse, inexpensive syringe made of already medically approved material. For the purposes of this invention the term single-use means that the maximum dosage placed into the syringe can only be administered one-time. The syringe, however, can administer medication multiple times, each time, however, delivering only a portion of the full medication capable of being drawn into the syringe by a single, full proximal drawing of the plunger rod. For short hand notation, the term single- use means and includes one or more possible uses, with each use delivering less dosage than the maximum. The cumulative total of delivered dosages obtained by all uses can not exceed the maximum dosage drawn into the syringe by a single, distal reciprocation of the plunger rod. The syringe is truly a one-time use syringe when the maximum dosage of the syringe (determined by the barrel capacity and/or the position of the spring clip on the plunger) is fully administered in its first usage. If that occurs, the spring clip is moved to its full distal position and all reuses are blocked. Where less than maximum is delivered on the first or succeeding dosage deliveries, the succeeding dosages administered are necessarily less than the maximum. There can be only one full distal movement of the plunger rod, to administer medication. In this manner, the device is a single-use syringe. The safe, one-time use and subsequent disposal of hypodermic needles and syringes are immediate concerns in the medical and health professions. Accidental needle stick injuries following use of a syringe pose a significant risk to patients, physicians and nurses. The risk is a source of great anxiety due to the current HIV and hepatitis infection concerns of the general public. Thus, extreme care must be taken in the safe handling and disposal of used needles and syringes. Toward this end, the present invention represents a single-use needle and syringe assembly. After the needle and syringe (hereinafter collectively referred to as the syringe) are once used, the mechanism of the present invention precludes further uses. It will, therefore, be more likely properly discarded than if further use were possible. Patient to patient cross contamination and drug user to drug user cross contamination are eliminated.
The present invention is compact and, therefore, is capable of being implemented into syringes of extremely small size barrel capacity including syringes capable of administering dosages as low as to 0.1 cc. The prior art, on the other hand, as will be more fully explained hereinafter, cannot be easily and/or economically downsized while maintaining the effectiveness of the one-time use only mechanism and, therefore, they have not been commercially introduced in sizes smaller than standard 3 cc syringe bodies. The axial location of the locking mechanism in the syringe barrel in the prior art single-use syringes was the means for limiting a 3 cc conventional syringe to a maximum 1 cc dosage. However, it is clearly desired to have smaller maximum dosage syringes where the size of the syringe, not only the location of the clip, determines the maximum dosage capacity. It should be appreciated, however, that the present invention can also be adapted for use with 3 cc or other maximum dosage syringe barrels and, yet, the present invention has particular applicability to syringes of low dosage capacity even those as low as 0.1 cc capacity.
It is generally recognized that a low cost syringe is essential to meet the needs of less developed countries and to contribute to the reduction of health costs everywhere. A low cost would mitigate syringe re-use now encountered with multiple-use disposable syringes. The cross contamination resulting from patient to patient reuse of the same syringe would be obviated by a single-use syringe. It would also reduce patient anxiety resulting from suspected potential infection from syringe use.
The present invention provides a simple and inexpensive to manufacture mechanism for limiting the usage of a syringe (with or without needle) to one-time or single-use only. The syringe is intended to be assembled at the manufacturing facility and provided to the physician (or nurse, patient, etc.) for use. The user fills the syringe with the appropriate medication in the conventional manner, i.e., by withdrawing the plunger with respect to the cylindrical barrel of the syringe, thereby drawing medication through the needle tip and into the chamber of the barrel. Then, again, using conventional technique, the needle is inserted to pierce the patient's skin. The plunger is manually moved with respect to the cylindrical barrel thereby forcing a piston toward the distal end of the syringe. The piston forces the medication out through the needle tip.
During the dosage administration portion of the procedure, according to the present invention, as will be more fully explained hereinafter, a locking spring clip travels along with the plunger shaft and, when it reaches the distal position, locking or contact points are held against the interior sidewall of the cylindrical barrel with the piston abutting the base of the locking spring clip. A second attempted retraction of the plunger with respect to the cylindrical barrel of the syringe is blocked. Thus, no further medication can be pulled into the syringe and, therefore, the syringe is incapable of being used a second time. A simple, inexpensive single-use syringe is provided. The locking mechanism, precluding reuse, is automatic, i.e., it operates to block reuse without a conscious operation by the user to engage its operation.
The design of an economically producible syringe assembly having the feature of single-use and whose safety or one-time use operation is difficult to defeat has been the subject of numerous patents and efforts. Such a syringe should be easy to manufacture and assemble, function in a standard manner, be able to deliver different volumes of fluid, utilize materials which are universally approved for medical use, preferably require standard equipment to manufacture such as used for making syringes in current use, and, importantly, be low in cost.
The present invention accomplishes the above objects by utilizing a new and unique plunger in association and in combination with a new and unique spring locking clip. The plunger comprises a plurality of cylindrical ratchet teeth. The spring clip is located by the manufacturer at a particular location on the plunger so as to limit maximum dosage of the syringe. In addition, the use of this new plunger and spring clip blocks reuse of the syringe. The construction can be incorporated into syringes of even 0.1 cc size without any loss of efficiency or safety. The operating mechanism of the present invention allows extremely small volumetric capacity of syringes to be manufactured, without loss of performance. In contrast, the locking mechanisms of prior art single-use syringes operate in different manners and, therefore, very small volume syringes cannot be manufactured. The present invention is economical to manufacture, has tamper-proof features, administers medication using conventional techniques, is made of medically approved materials, and can be made with standard equipment.
It is a feature of the present invention to provide the thumb-contacting portion of the syringe plunger as a break-apart disc such that, after use, the user of the syringe can simply bend or twist and remove the thumb-contacting disc and, thereby, further disable the syringe from a subsequent reuse. The ability of the thumb-contacting portion of the plunger shaft to become disengaged from the syringe also serves as a means for tracking inventory of the syringes.
It is another feature of the present invention to provide another mechanical locking mechanism. This feature, as well, blocks a second use of the syringe. It engages, however, only when the user deliberately desires to do so, by fully reciprocating the plunger to its maximum distal position. To effect this mechanical lock, the plunger and the thumb-contacting disc portion must be pushed fully toward the distal end of the syringe. When moved as described, the thumb-contacting disc portion and the plunger are locked (incapable of being withdrawn to draw in additional medication) by the interaction of an annular male dove-tail of the plunger which cooperates with an annular female dove-tail of the barrel. Here, too, a safety mechanism is provided to prevent reuse of the syringe.